In a large mixing bowl, combine the butter, sugar, and baking powder. Begin mixing on low speed until well blended. Increase to medium-high speed and continue beating until the mixture becomes light and fluffy. Add the egg and almond extract, ensuring everything is well incorporated. Reduce the speed to low and gently mix in the flour and cornstarch until just combined, being careful not to overmix.
1/2 cup (1 stick) unsalted butter, 1 cup granulated sugar, 2 teaspoons baking powder, 2 large eggs, 1/2 teaspoon pure almond extract, 1 2/3 cups all-purpose flour, 1/4 cup cornstarch
Divide the dough into two equal portions, shaping each into a disc approximately 1 inch thick. Individually wrap each disc in plastic wrap and refrigerate for a minimum of 4 hours, or until the dough is firm enough to be rolled out.
Preheat the oven to 350°F. Prepare a heart-shaped cookie cutter for the dough. A 5-inch cutter is recommended, but a smaller size, such as 2 1/2 inches, can also be used based on your preference.
On a lightly floured surface, roll out one dough disc (keep the other in the refrigerator) to approximately 1/8-inch thickness, using a floured rolling pin to ensure an even surface. Cut out shapes with a heart-shaped cookie cutter. Transfer the cut dough, still on the wax paper, to a baking sheet and place in the freezer for 5 to 10 minutes until firm and easier to handle.
Carefully peel the heart shapes off the wax paper and place them 1 inch apart on an ungreased baking sheet. Using a butter knife, make a 2 3/4-inch slit in the center of each heart and gently spread them apart to form wings. Lightly brush the tops with egg white, press almonds into the dough, and sprinkle with a bit of sugar. Bake for 8 to 10 minutes, or until the edges turn a light golden brown. Transfer to a wire rack to cool completely.
2 large eggs, sliced almonds, raw sugar